1. Field of the Invention
The present invention relates to a rolling-element hold spacer for retaining, in a rotatable and slidable manner, rolling elements used in a rectilinearly-movable apparatus, such as a rectilinearly-rolling guide apparatus, a ball screw, and a ball spline, as well as a rectilinearly-movable apparatus using the rolling element hold spacer.
2. Description of the Related Art
As shown in FIG. 15, a single-element retainer 2 for individually holding a ball 1 has already been known as a rolling-element hold spacer for a holding ball (corresponding to a rolling element) used in a rectilinearly-movable apparatus (see, for example, Japanese Patent Publication No. 33774/1993). The ball 1 is held, in a rotatable and slidable manner, within a housing hole 2a formed in the single-element retainer 2 while the upper and lower portions of the ball 1 are partially exposed. The single-element retainer 2 is incorporated in the rectilinearly-movable apparatus. A fittingly-insert section 2b is bulgily formed in the single-element retainer,2 on either side of the ball 1 and is to be inserted into a guide channel formed in a slide member. The single-element retainers 2, each housing the ball 1, are inserted in a circulation path of the slide member. The single-element retainers 2 travel in the direction designated by A shown in the drawing. The opposite ends of the single-element retainer 2, which come into contact with the corresponding ends of the adjoining single-element retainers 2 while the single-element retainers 2 are traveling along the circulation path, are formed so as to assume a circular-arc shape 2c. The distance between the centers of the adjacent balls 1 is maintained constantly. Since the balls 1 are arranged and held in a circulation path while being held by the respective single-element retainers 2, the balls 1 are prevented from rubbing against each other during circulation, thus preventing generation of a collision sound or abrasion, which would otherwise be caused by rubbing action.
Such a known single-element retainer 2 is suitable for being arranged and housed in the circulation path of the rectilinearly-rolling guide apparatus, as well as for effecting two-dimensional change between linear travel direction A and U-shaped travel direction B, as shown in FIG. 15. However, there may be a case where a ball screw requires three-dimensional change of direction and torsional movement with respect to a travel direction, as well as two-dimensional change of direction. The single-element retainer 2 is difficult to effect such complicated movements. Further, the circumference of the ball 1 exclusive the upper and lower portions thereof is covered with the single-element retainer 2. It is difficult for a lubricant to enter the space between the single-element retainer 2 and the ball,thus insufficiently lubricating the ball 1. Further, since one single-element retainer 2 is used for holding a single ball 1, space for the circular-arc portions 2c of the adjacent single-element retainers 2 must be ensured between the adjacent balls 1. For this reason, the single-element retainers 2 occupy space within the circulation path, thus imposing a limitation on the number of balls 1 to be inserted into the circulation path. Therefore, the rectilinearly-rolling guide apparatus cannot assume a large load-carrying capacity. The portion of the single-element retainer 2 which comes into contact with the corresponding portion of the adjacent single-element retainer 2 assumes a circular-arc protrudent shape 2c, and hence the adjacent single-element retainers 2 come into substantial line contact with each other, thus increasing a contact pressure. Consequently, there is a case where the single-element retainers 2 repeatedly come into collision with each other during the course of circulating operation, thus causing a collision sound. Further, the single-element retainer 2 has the bulgily-formed fittingly-insert sections 2b and hence has an irregular thickness with respect to the circulating direction of the single-element retainer 2 (i.e., direction A). Therefore, the single-element retainers 2 may cause pitching during a circulating operation.